Tantalum η2‑Vinyl Complexes Bearing an [η5:σ-Me2C(C5H4)(C2B10H10)]2– Ligand: Syntheses and Structural Characterizations

Transition-metal η2-vinyl complexes, also known as 1-metallacyclopropenes, constitute an important subset of metal alkenyl complexes, which are limited to groups 6–8 metals only. We report in this paper a strategy for the synthesis of Ta η2-vinyl complexes. Hydrogenolysis of tantalum alkyl complex LTaMe3 (1, L = [η5:σ-Me2C­(C5H4)­(C2B10H10)]) in the presence of dmpe ([Me2PCH2]2) followed by addition of p-tolylacetylene gave an η2-vinyl complex, LTa­(η2-H2CCC6H4CH3)­(dmpe) (2). Replacement of p-tolylacetylene with t-butyl acetylene resulted in the formation of an alkynyl η2-vinyl complex LTa­(η2-HCC t Bu)­(Me2PCH2CH2PMe2)­(CC t Bu) (3). Using trimethylsilyl acetylene as the substrate gave both LTa­(η2-H2CCSiMe3)­(dmpe) (4) and LTa­(η2-HCCSiMe3)­(Me2PCH2CH2PMe2)­(CCSiMe3) (5). A mechanistic study revealed that the Ta η2-vinyl complexes 2–5 were formed through a tantalum trihydride intermediate, which was trapped by CO to give LTaH­(CO)­(dmpe) (6).